All i want to do is scale an image vertically
If you introduce a reference using the 'Background Image' mechanism, I'm fairly sure you can't scale it non-uniformly, or about a chosen origin.

You can, though, by introducing the image as an object, either by creating an  'Image' Empty, or by importing 'Images as Planes'. In both cases you could snap the cursor to your desired stationary point on the model (Edit Mode, ShiftS, > Cursor to Selected), then switch to the image, and, say, SY, with the Pivot Center set to the cursor.